A switching unit, which is activated with the aid of a driver circuit, is used to activate an electrical consumer, to enable a current flow between the consumer and a predetermined potential. To keep waste heat low and electromagnetic compatibility high, it is possible to activate the switching unit for controlling the consumer current using a current source instead of using a voltage source. If the current source is activated, it thus delivers a predetermined control current to the switching unit, which permits a current flow through the consumer as a function of the control current. If the switching unit is constructed with the aid of a bipolar transistor, a current flow may thus be controllable in an analog manner as a function of the control current; in a specific embodiment having a field-effect transistor, another relationship may exist.
It is possible that the current source degrades on the basis of a thermal stress or an aging effect, that is to say, the control current provided thereby is excessively large or excessively small. It is then a concern that the switching unit will be overloaded, so that it may be damaged, or will not be sufficiently activated, so that it enables the current to move through the consumer excessively slowly or not at all. In a safety-critical application, for example, for activating an electric motor as a steering aid in a motor vehicle, the activation must meet specific reliability and safety requirements. Such requirements are stipulated, for example, in the specification ASIL (automotive safety integrity level) corresponding to ISO 26262.